Decompression device for internal combustion engines

ABSTRACT

A decompression device for an internal combustion engine in which the control parts which open and close the exhaust valves of the combustion chambers include a rocking lever acting on the valve. The decompression device includes an eccentric bearing on which the rocking lever is freely mounted, rotation of the eccentric bearing thus moving the axis of the rocking lever to prevent full closing of the exhaust valve, that is, provide decompression of the chamber. The eccentric bearing may be turned to reference position at which it permits full closing of the exhaust valve by either manual or automatic means.

United States Patent 1191 Hatz [ DECOMPRESSION DEVICE FOR INTERNALCOMBUSTION ENGINES [75] Inventor: Ernst Hatz, Ruhstorf, Germany [73]Assignee: Motorenfabrik Hartz KG., Germany 22] Filed: Mar.29, 1971 211App]. 196.; 128,942

[30] Foreign Application Priority Data 3,146,772 9/1964 Hatzm, ..l23/l821451 May 29, 1973 Primary Examiner-Laurence M. Goodridge AssistantExaminer-Ronald B. Cox Attorney-Larson, Taylor & Hinds [5 7 ABSTRACT Adecompression device for an internal combustion engine in which thecontrol parts which open and close the exhaust valves of the combustionchambers include a rocking lever acting on the valve. The decompressiondevice includes an eccentric bearing on which the rocking lever isfreely mounted, rotation of the eccentric bearing thus moving the axisof the rocking lever to prevent full closing of the exhaust valve, thatis, provide decompression of the chamber. The eccentric bearing may beturned to reference position at which it permits full closing of theexhaust valve by either manual or automatic means.

5 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION This inventionrelates to internal combustion engines, and in particular it relates toa decompression device for an internal combustion engine.

In internal combustion engine of the type having exhaust valves for thecombustion chambers controlled by rocking levers and push rods, a meansis often provided to prevent full closing of the exhaust valve to permitdecompression or at least prevent a high level of compression whichwould impede the starting of the engine. The exhaust valves are normallycontrolled by a system of control parts which transmit engine motion tovalve movement. In conventional decompression devices, a decompressioncam is arranged to act on one of the control parts. It is often turnableeither by hand or by an automatic means to terminate decompression.

In known decompression devices of this kind, the control part usuallycarries an adjustable screw which bears on the decompression cam sothatthe amount of decompression travel of the exhaustvalve can be adjustedat will by varying the setting of the adjusting screw. By inappropriateuse through unfamiliarity with operating conditions, it is thereforepossible for the decompression travel to be set to exceed the maximumpermissible amount with resulting serious drive failures or damage tothe control parts.

Moreover, previously known decompression devices 'have had the furtherdisadvantage that, at certain times during decompression movement theengagement within the system of control parts is momentarilyinterrupted. For example, in internal combustion engines 7 with ahydraulic valve clearance adjusting device in the push rod, theclearance which exists during interruption of the control engagementbetween the rocking lever and the push rod causes the push rod to extendso that the decompression cannot be terminated.

Thus, there exists a need for a new and improved decompression devicewhich will overcome these disadvantages of the prior art.

SUMMARY OF THE INVENTION It is a purpose of the present invention toprovide a new and improved decompression device for an internalcombustion engine, which device overcomes disadvantages of the priorart.

This purpose of the present invention is achieved by providing anarrangement in which the maximum opening of the exhaust valve duringdecompression can be limited and controlled, and in which engagementbetween the control parts of the control system is permanently insured,especially the power connection between the push rod and the rockinglever.

These problems are solved in accordance with the present invention byproviding an arrangement in which the decompression cam is in the formof an eccentric bearing forming a mounting about which the rocking leverrocks, thus varying the position of the rocking lever axis which in turnsets a-maximum decompression opening of the subject valve, such that theposition of the-eccentric bearing determines the magnitude of thedecompression opening. The maximum decompression opening is defined asthat opening which willbe maintained even when the system of controlparts normally would permit the valve to close all i the way were it notfor the decompression device.

In a simple embodiment of a decompression device in accordance with thepresent invention, a means may be provided for controlling the eccentricbearing by hand, thus shutting off the decompression device at aconvenient time such as when the engine has heated up sufficiently.

It is also a feature of the present invention to provide a device forautomatically terminating decompression. In such a device forautomatically terminating decompression, a toothed disc may be providedfor rotational movement with the eccentric bearing. A suitable meanswhich undergoes oscillatory movement upon normal operation of the enginemay then be operatively connected to the toothed disc to turn the sameduring each oscillation thereof. For example, this suitable means may bea rocking lever controlling the inlet to the combustion chamber. Thesuitable means may be connected to he toothed disc by a driving membercomprising a spring-tongue which engages the toothed disc and is biasedradially inwardly relative thereto but which can be sprung outwardly topermit stepwise turning of the toothed disc, and hence stepwise turningof the eccentric bearing, the latter thus returning to its originalposition at which decompression is terminated. In an advantageousarrangement, the disc is mounted on the same shaft as the eccentricbearing and the rock ing lever of the valve being controlled.

Thus, it is an object of this invention to provide a new and improveddecompression device for an internal combustion engine, which deviceovercomes the disadvantages of the prior art.

It is another object of this invention to provide a new and improvedinternal combustion engine decompression device in which maximumdecompression can be controlled while eliminating the danger ofmaintaining unacceptably high decompression.

It is another object of this invention to provide for an internalcombustion engine a decompression device in which the control partswhich operate the decompression device are not interrupted during theoperation of the decompression device.

Other objects and the intended advantages of the present invention willbecome apparent from the detailed description to follow, together withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS There follows a detailed'descriptionof preferred embodiments of the invention to be read together with theaccompanying drawings.

FIG. 1 is a sectional view of a portion of an internal combustion engineshowing the decompression device constructed in accordance with thepresent invention.

FIG. 2 is a plan view of FIG. 1.

FIG. 3 is an enlarged sectional view taken along line III-III of FIG. 2.

FIG. 4 is a sectional view similar to FIG. 3 but showing the device in adifferent operative position.

FIG. 5 is a plan view of a simple construction of the decompressiondevice which can be operated manually.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings, like numerals represent like elements throughout the severalviews.

An exhaust valve 2 is provided in a valve housing 1 of afour strokeinternal combustion engine of known form and is biassed upwardly againsta valve seat 4 under the influence of a closing spring 3. A push rod 5,which is moved up and down by a non-illustrated control drive, engages adouble-armed rocking lever 6 for moving the exhaust valve 2 downwardlyin the open direction. The valve 2 is opened by upward movement of thepush rod 5, while it is closed under the action of its spring 3 duringupward movement of the same.

A mounting shaft 7 is mounted in the valve housing 1' and carries aneccentric bearing 7a, on which a boss 6a of the rocking lever 6 ismounted for free turning movement. Accordingly, during operation of thevalve, the rocking lever 6 performs a to and fro turning movement on theeccentric bearing 7a.

Fitted to a projecting end 7b of the mounting shaft 7 is a hand grip 8by which the mounting shaft can be turned about its longitudinal axis toadjust the position of its-eccentric bearing about the axis of themounting shaft. Thus, the eccentric bearing 7a can be moved from itsnormal drive position shown in FIGS. 1 and 3, into the position of FIG.4, in which decompression of the combustion chamber is effected. Thatis, when the eccentric bearing 7a is positioned as shown in FIG. 4, theaxis of rotation of the rocking lever 6 has been lowered while the restposition of the push rod 5 has remained the same, as a result of whichthe valve 2 cannot fully close against its seat 4. Rather, in theuppermost position of the valve 2 it will remain separated from its seat4 by the distance H as shown in FIG. 1 which corresponds to the distanceE of movement of the axis of the rocking lever 6 which resulted frommovement of the eccentric bearing 7a from the FIG. 3 position to theFIG. 4 position. As a result, the combustion chamber with which thevalve 2 is associated does not fully close. Thus, in accordance with thepurpose of a decompression device, full compression does not occurwithin the chamber, which full compression would impede the starting ofthe engine. Specifically, this movement of the eccentric bearing 7aresults from turning the hand grip 8 from the position of FIGS. 1 and 3into the position of FIG. 4. The end 6b of the rocking lever 6 issupported by abutment with the push rod 5 so that the other end 6cswings downwardly through an angular amount, the maximum extent of whichis determined by the eccentricity E of the eccentric bearing 7a. Adecompression travel smaller than H can of course be set if theeccentric bearing 7a, when set to decompression, is adjusted, notthrough 180 as shown in FIG. 4, but through a smaller angular amount.

In the embodiment according to FIGS. 1 to 4, the device is also providedfor automatically terminating the decompression. This comprises a drivedisc 9 which is fitted to the mounting shaft 7, the boss 9a of the drivedisc 9 being, for example, fitted to the mounting shaft 7 by a taperedpin 10. The drive disc 9 is provided around its periphery with inclinedteeth 9b. The drive disc 9 is completely toothed around its periphery,except for a gap 90.

A rocking lever 11 for the inlet valve of the combustion chamber ismounted for free turning on the central part of the mounting shaft 7,being operated in similar fashion to rocking lever 6 from the controldrive. Fitted to the rocking lever 11, e.g. by screws, is a springtongue 72 which extends in the axial direction of the shaft 7. The endof this tongue operates as a driver 12a for the teeth 9b on the drivedisc 9. Thus, during engine operation, the driver 12a and rocking lever11 perform an oscillating to and fro turning motion through apredetermined, fixed angular amount A.

When the engine is either completely off or running normally, thedecompression device is in the position of FIG. 3. Upon movement of therocking lever 11 in the clockwise direction, the driver 12a cannotengage the toothing 9b because of the gap 9c, because the gap 9c lieswithin angle A. Both valves operate normally, i.e., opening and closingcompletely. If, on the other hand, a stationary engine is to be startedup with the aid of the decompression device, the mounting shaft 7 ismoved in the clockwise direction by the hand grip 8 to turn theeccentric bearing 7a. If maximum decompression travel is required atthis time, this setting movement is through so that the components aremoved from the position of FIG. 3 to the position of FIG. 4. Theuppermost position of the end 60 of the rocking lever 6 is thereforemoved down and the exhaust valve 2, in its uppermost position remainsopen by an amount H, as it moves from its closed position 0 to itsdecompression position D. When the engine is turned over and the pushrod 5 moved upwards, the exhaust valve is accordingly opened furtherfrom the decompression position D until it reaches position V(completely open). When closing, however, the exhaust valve 2 does not,on the other hand, return completely to the closed position 0, but onlyto the decompression position D. (The positions D and V indicatedschematically in FIG. 1 are not in corresponding proportions; inpractice, the decompression travel II will be approximately 1 mm. andthe opening travel approximately 10 mm.).

During the portion of each oscillation when the parts move in directionX, the rocking lever 11 moves the drive disc 9 through an angular amountA by means of its driver 12a, so that the drive disc 9 and the shaft 7coupled thereto, together with the eccentric 7a are also moved in thisdirection. During the return movement of rocking lever 11 and driver 12ain direction Y, the drive disc 9 remains stationary and the driver 12aslides back in spring action over the adjacent tooth and occupies a newdrive position in front of the next tooth 9b. This sequence is repeateduntil the driver 12a has engaged all he teeth 9b stepwise and it engagesgap 9c. The mounting shaft 7b together with the drive disc 9 againoccupy the positions of FIG. 3. The decompression movement is decreasedin steps from the maximum amount H in FIG. 4 until it again becomes zeroin the position of FIG. 3, i.e., the exhaust valve 2 opens and closes asnormal.

It is up to the discretion of the operator to set the duration of thedecompression and also the point at which the decompression isterminated. With the setting according to FIG. 4 the maximumdecompression and therefore the longest time is set. If, on the otherhand, the drive disc is moved in the clockwise direction from theposition of FIG. 3, for example, through 270, for about half thedecompression travel H, the driver 12a cooperates step by step with lessteeth 9b and so that termination occurs more quickly.

The rest position of the shaft 7, at the top dead center 1 position ofthe eccentric bearing 7a as shown in FIGS.

1 and 3, is stable because the re-setting forces acting on the rockinglever 6 tend to hold the parts in this position. If necessary, themounting shaft 7 could be held in the position of FIGS. 1 and 3 by astop. Equally, a safety device, e.g. a ratchet device, could be providedto allow setting movement of the drive disc 9 in one direction only, (inthe clockwise direction according to the drawing because of the toothform). Moreover, an indicator is preferably associated with the handgrip 8, which gives, on a fixed scale, both the setting direction andthe set amount ofdecompression travel. Finally, it is possible toprovide, around the periphery of the drive disc 9, an additional, largergap in which the driver 12a does not drive. In this region permanentdecompression exists (decompression for a period of selected duration)should the-operator turn the eccentric 7a so far that the driver 12aengages in this additional gap. The permanent decompression ispreferably used to ventilate or turn the engine freely in extreme cold.

Obviously, a construction can be provided in which the termination ofdecompression can be effected by hand only as shown in the embodiment ofFIG. 5. Here, the drive elements 9 and 12 are omitted, while themounting of the rocking lever 6 on the eccentric bearing 7a of themounting shaft 7 is retained in similar fashion. The other rocking lever(11) is separately mounted and no longer influences the first rockinglever 6 so that the operator must, in this embodiment, move the elementsof the decompression device by hand by means of grip 8, from the normalposition of FIG. 1 into the decompression position, and, after thestarting procedure has been carried out, must return them by hand fromthe decompression position, to the normal position of FIG. 1. (In thiscase, a release, per haps a reset spring associated with the hand grip8, is sufficient).

Although the invention has been described in considerable detail withrespect to the preferred embodiments thereof, it will be apparent thatnumerous modifications and variations apparent to those skilled in theart are possible within the spirit and scope of the invention.

I claim:

1. A device for decompressing a combustion chamber of an internalcombustion engine of the type in which the chamber has an exhaust valve,a rocking lever mounted on a mounting shaft for movement thereabout tooperatively engage the exhaust valve to open the same, and a closingmeans for closing the valve in the absence of an opening force appliedby the rocking lever, said device comprising: a decompression cam in theform of an eccentric bearing mounted on said mounting shafteccentrically relative to the axis of the-mounting shaft and forrotation with the mounting shaft, said rocking lever being freelymounted on the eccentric hearing such that rotation of the eccentricbearing varies the position of the axis of rotation of the rockinglever, said eccentric bearing being positioned and shaped such that inat least one position the exhaust valve is permitted to close all theway, an in a plurality of other positions the rocking lever prevents theclosing member from closing the exhaust valve all the way, thusproviding a decompression opening of the chamber, a setting membermounted to actuate the mounting shaft to rotate said eccentric bearingto any one of a plurality of angular positions to set the rocking leverto any one of said plurality of other positions including a maximumdecompression valve opening position or any one of a plurality of valveopening positions between the maximum opening and the valve closedposition, the magnitude of this decompression opening being variable atwill and dependent on the angular position of said setting member andthus on the angular position of the eccentric bearing, and a returnmeans for automatically turning the eccentric bearing from the saidother positions to said one position in response to operation of theinternal combustion engine, said return means comprising a toothed discmounted for rotational movement with the mounting shaft, and a membermounted for oscillating movement upon normal operation of the engine,said member being operatively engaged with the teeth of the disc to turnthe disc in steps by engaging and turning one tooth during each of saidoscillations.

2. A device according to claim 1, said setting member including a handlegrip fixedly connected relative to said eccentric bearing to turn theeccentric bearing and the mounting shaft about the axis of the latter atwill to one of said plurality of angular positions.

3. A device according to claim 1, wherein said member is an oscillatinglever mounted to rotate freely about the said mounting shaft andcontrollable to operate an inlet valve of the said chamber, and a springtongue element connected to the oscillating lever and engaging the teethof the discs, such that in one direction of movement of the oscillatinglever, the tongue turns the disc and the mounting shaft, and in theopposite direction it is sprung out of contact with the disc.

4. A device according to claim 3, wherein the said disc is fixed to themounting shaft immediately adjacent the said rocking lever.

5. A device according to claim 1, wherein said memher is an oscillatinglever, and including a spring tongue element connected to theoscillating lever and engaging the teeth of the discs, said tongue beingbiassed radially inwardly relative to the disc and sufficientlyresilient to pass over the teeth, such that in one direction of movementof the oscillating lever the tongue turns the disc and mounting shaftand in the opposite direction it is sprung out of contact with the disc.

1. A device for decompressing a combustion chamber of an internal combustion engine of the type in which the chamber has an exhaust valve, a rocking lever mounted on a mounting shaft for movement thereabout to operatively engage the exhaust valve to open the same, and a closing means for closing the valve in the absence of an opening force applied by the rocking lever, said device comprising: a decompression cam in the form of an eccentric bearing mounted on said mounting shaft eccentrically relative to the axis of the mounting shaft and for rotation with the mounting shaft, said rocking lever being freely mounted on the eccentric bearing such that rotation of the eccentric bearing varies the position of the axis of rotation of the rocking lever, said eccentric bearing being positioned and shaped such that in at least one position the exhaust valve is permitted to close all the way, and in a plurality of other positions the rocking lever prevents the closing member from closing the exhaust valve all the way, thus providing a decompression opening of the chamber, a setting member mounted to actuate the mounting shaft to rotate said eccentric bearing to any one of a plurality of angular positions to set the rocking lever to any one of said plurality of other positions including a maximum decompression valve opening position or any one of a plurality of valve opening positions between the maximum opening and the valve closed position, the magnitude of this decompression opening being variable at will and dependent on the angular position of said setting member and thus on the angular position of the eccentric bearing, and a return means for automatically turning the eccentric bearing from the said other positions to said one position in response to operation of the internal combustion engine, said return means comprising a toothed disc mounted for rotational movement with the mounting shaft, and a member mounted for oscillating movement upon normal operation of the engine, said member being operatively engaged with the teeth of the disc to turn the disc in steps by engaging and turning one tooth during each of said oscillations.
 2. A device according to claim 1, said setting member including a handle grip fixedly connected relative to said eccentric bearing to turn the eccentric bearing and the mounting shaft about the axis of the latter at will to one of said plurality of angular positions.
 3. A device according to claim 1, wherein said member is an oscillating lever mounted to rotate freely about the said mounting shaft and controllable to operate an inlet valve of the said chamber, and a spring tongue element connected to the oscillating lever and engaging the teeth of the discs, such that in one direction of movement of the oscillating lever, the tongue turns the disc and the mounting shaft, and in the opposite direction it is sprung out of contact with the disc.
 4. A device according to claim 3, wherein the said disc is fixed to the mounting shaft immediately adjacent the said rocking lever.
 5. A device according to claim 1, wherein said member is an oscillating lever, and including a spring tongue element connected to the oscillating lever and engaging the teeth of the discs, said tongue being biassed radially inwardly relative to the disc and sufficiently resilient to pass over the teeth, such that in one direction of movement of the oscillating lever the tongue turns the disc and mounting shaft and in the opposite direction it is sprung out of contact with the disc. 